The present invention relates to a control apparatus of a gasoline engine, and more particularly to a control apparatus suitable for reducing an amount of emission of so-called particulate matters (PM) in a direct injection gasoline engine.
The direct injection gasoline engine has a problem that it has a larger amount of PM emission than an intake port injection type gasoline engine. The causes of this problem are fuel adhesion to a cylinder and a piston due to direct injection of fuel into the cylinder, and existence of local fuel rich regions caused by insufficient mixing of fuel and air. Therefore, as measure for reducing the amount of PM emission in the direct injection gasoline engine, it is effective to reduce an amount of fuel adhesion and to promote mixing of fuel and air.
As technique to suppress the amount of PM emission in the direct injection gasoline engine, technique is known in which hot exhaust gas is made to exist in the combustion chamber during engine cold start upon which the amount of PM emission is large, that is, technique in which the vaporization of the fuel is promoted by introducing internal EGR (Exhaust Gas Recirculation) and thereby emission of black smoke is reduced (JP-A-2002-327651).
However, not only the amount of PM emission during engine cold start but also the amount of PM emission after the engine is fully warmed up cannot be neglected. In particular, the amount of PM emission is increased during acceleration operation in which air-fuel mixture in the cylinder is likely to be in a fuel rich state due to the difference in control responsiveness between air and fuel. Further, there is a problem that the amount of PM emission is increased during acceleration operation because, even when parameters of respective engine devices (for valve operation, for fuel injection, for ignition, and the like) are set to reduce the amount of PM emission, combustion chamber transiently passes through a state different from desired state due to a parameter providing a slow response. Therefore, in order to reduce the amount of PM emission at the time of acceleration operation, it is necessary to sufficiently take into consideration the transient responsiveness of each of the devices.
In view of the above described problems, an object of the present invention is to provide a control apparatus of a direct injection gasoline engine, the control apparatus being capable of reducing the amount of PM emission even during acceleration operation in which the air-fuel ratio in the cylinder is likely to be in a fuel rich state.